5mm colour changing LED (High Brightness)

Inside the colour changing LED is a microcontroller and a red, green and blue LED. What the microcontroller does is turn the three LEDs on and off very quickly and depending on if a colour is on for longer than it is off will determine the brightness of that colour. This means that the amount of the red, green and blue can be varied and a whole range of colours are available. Thus the LED is able to slowly cycle through the various colours. The voltage does have an effect on the brightness but not really the speed.

A video of the product in action is available on the link at the bottom of the description. We have recently added a 10mm version which is now shown in the related items section on the left.

If you use two AA batteries then when they are brand new there will be 3.2V across them both. This quickly drops to 3V hence the 1.5V per cell value. The problem is that for the rest of the batteries life the voltage slowly drops from 1.5V down to 1V. So if you want to get the most out of the two batteries then you will only have 2V across both of them at the end of their life. Since the colour changing LED is only rated down to 2.7V you will only be using 30% of the batteries capacity. With this in mind I’m going to do the sums for 3x AA batteries as 100% off the batteries capacity will be used.

A good alkaline battery has a capacity of 1500mA/h, which means that if you draw 1500mA out of the battery it will last 1 hour. The current taken by the colour changing LED will vary depending on colour and battery voltage, but let’s assume a current of 25mA. So the battery capacity is 1500mA/h divided by the current (25mA) so it will last for 60 hours. A cheaper zinc carbon battery will probably be half this amount. This is based on using 3 AA batteries.

If only 2 AA batteries are used then they will last for less than 20 hours with alkaline batteries and less than 10 with zinc carbon batteries.

The LEDs typically take about 25mA, however some colours require more current than others, it could peak at 50mA so it’s best to use that for max current calculations. So with 30 LEDs you should allow for 1.5A current (this is at 5V). You can reduce the brightness and therefore current by bringing the voltage down, running at 4.5V would use less power than at 5V.

Each LED has a small computer in it and runs off a clock driven by a resistor capacitor network. As a result the timing of one LED will be different to another LED. We have a sign that we use at shows that has 36 colour changing LEDs in it. To get them in sync I had to take a bigger batch of LEDs and power them up and take out the ones that were too fast or too slow. Doing this you can keep the LEDs within a second or two of each other for the complete cycle. The sequence starts and finishes on red and if you turn all the LEDs off for a fraction of a second at the end of the sequence the computer in them will reset and the timings will be resynchronised. The human eye won’t see the LEDs go off. If you don’t resynchronise the LEDs they will all be on different colours after about 10 minutes.

It’s exactly the same LED in the centre of the package in both cases, it is just a case that one is 5mm in diameter and the other is 10mm in diameter. They both cycle the same pattern at the same brightness, some people find the larger LED is better for what they are doing and others will go for the smaller one.

The colour changing LED requires a DC voltage of 2.7 to 5V to operate and then cycles through a pre-determined pattern. As it takes a variable amount of current depending on the colour, it is not possible to reduce the voltage across a current limit resistor. So no it can’t be connected as the voltage is both too high and alternating.

If you want to be able to control the colour of an LED then you would want to get an RGB LED that contains three separate LEDs see:
http://www.kitronik.co.uk/products/components/leds/leds/colour-changing-and-rgb-leds/rg

The max reverse voltage on this part is 5V so don’t use it with an AC supply (even with a current limit resistor).

The only thing to watch out for is in a worst case scenario the LED takes more current for certain colours, if they were all in sync which they could be briefly at the start then you should use a max working current of 50mA per LED. So worst case 5 LEDs would be 250mA. Now the USB port allows devices to take 100mA as standard, however the device can talk to the computer and ask for up to 500mA. The computer then make a decision based on what else is connected as to whether a higher current is allowed. Clearly the colour changing LEDs can’t ask for more current so you will need to decide if it’s going to be OK before plugging it in. If nothing else is connected to the computer then it will be fine.

You don’t need a current limit resistor with these LEDs as long as they are being driven in the right voltage range. The LED is designed to run from 2.7 to 5 V and this can’t be done by a current limit resistor as the LED takes different amounts of current depending upon the colour that is being displayed. Most modern phone chargers are 5V and have a mini USB plug on them, older chargers that don’t have a USB style plug won’t necessarily be 5V. If you don’t have a 5V supply then you would just want to use a 5V regulator to make a 5V supply, these are inexpensive and simple to use, for more info see:
http://www.kitronik.co.uk/products/components/semiconductors/integrated-circuits-ic-s/7

Once you have either determined that you have a 5V supply or regulated to 5V you then want to connect the LEDs in parallel, so all the flat edges connect together and to 0V and all the other leads connect together and to 5V.

Hi George,

Can I ask how you connected the LEDs? Where in the circuit are they?
The amount of current the LEDs draw varies as they change colour and this is likely causing the power supply to fluctuate which in turn is upsetting the IC as it tries to decode the radio signals.

Are you powering the circuit from a battery or the mains? Is it one of our FM radio kits?